Electron-beam-induced responses of biologically relevant organic molecules

Abstract

Cathodoluminescence (CL) properties of biologically relevant organic molecules were systematically investigated under electron beam irradiation to elucidate electron–matter interactions in soft molecular systems. Aromatic amino acids (D- and L-tryptophan, tyrosine, and phenylalanine), coenzymes (NADH and FAD), and carbohydrates (glucose, glycogen, and sodium glucose-6-phosphate) were examined in vacuum using a scanning electron microscope equipped with a CL detection system. Among the molecules studied, aromatic amino acids exhibited significantly stronger CL emission than coenzymes and carbohydrates. In particular, L-tryptophan showed the highest CL intensity with a dominant visible emission band around 570 nm. The spectral origin of this visible band appears distinct from the conventional near-UV fluorescence of intact tryptophan and may involve solid-state or modified tryptophan-related emissive states. Time-dependent CL measurements under continuous electron beam irradiation revealed distinct behaviors depending on molecular structure. While the CL intensity of L-tryptophan gradually decreased and that of L-tyrosine remained relatively stable, L -phenylalanine exhibited a pronounced increase in CL intensity accompanied by a blue shift of the emission peak from approximately 500 nm to 430 nm. The irradiation-induced enhancement and spectral shift observed in phenylalanine suggest changes in the relative contributions or efficiencies of different emissive states under continuous electron-beam irradiation. These results highlight that organic CL properties strongly depend on molecular structure and irradiation history. The present findings provide experimental insight into how electron beam irradiation modifies the luminescence responses of biologically relevant organic molecules and demonstrate that CL can serve as a useful readout for evaluating irradiation-induced changes in soft organic molecular systems.

The authors' abstract, as published at the source. Results in Chemistry, 2026 · DOI ↗